RBF And GFR

Question 1

The kidneys receive 1/4 of the entire cardiac output. Why?

Answer 1

They need high flow to support filtration.

Not because they are super metabolically active

Question 2

How do you calculate the Filtration Fraction?

Answer 2

GFR
FF= _________
RPF

(Plasma flow, not blood)

Question 3

How do you calculate renal plasma flow?

Answer 3

RPF= (1-Hct)RBF

(1-Hct) gives you the amount of blood that is plasma, so this makes sense

Question 4

What effect will angiotensin II, ADH, ATP and endothelin have on RBF and GFR

Answer 4

Decreased

Although the effects of ATII on GFR are variable

Question 5

Which arteriole is more sensitive to angiotensin II at lower concentrations?

Answer 5

Efferent arteriole

so when you have a low concentration of ATII, you reduce RBF, but maintain GFR

Question 6

What effects will atrial natriuretic peptide, glucocorticoids, NO and prostaglandins have on RBF and GFR?

Answer 6

Increase

Question 7

Does the blood flow and GFR remain constant when your blood pressure changes?

Answer 7

Yes, the kidney AUTOREGULATES as long as the pressure is between 80-180mmHg.

Question 8

Can the autoregulation of RBF and GFR be overridden?>

Answer 8

Yes, large increases in SNS tone or severe blood loss will decrease RBF and GFR

Question 9

What are the 2 mechanisms the kidney uses to autoregulate its blood flow and GFR?

Answer 9

1. Myogenic mechanism- the vascular smooth muscles will contract if they stretch too much
2. Tubuloglomerular feedback (“flow dependent”)- if GFR increases, more NaCl will flow through the LOH, and the macula densa will sense it and cause the afferent arteriole to contract, thus decreasing RBF and GFR

Question 10

How does the macula densa help the nephron maintain a constant GFR and RBF?

Answer 10

It maintains a constancy of SALT load delivered to the distal tubule

Question 11

True or false:

The fluid in Bowman’s capsule is essentially a protein-free filtrate of blood plasma

Answer 11

True

Everything in the blood except for the proteins gets filtered out initially

Question 12

In the filtration barrier, there are 3 layers: the endothelial cells of the capillary, the basal lamina, and the podocytes/slits.
Which ones are the barriers to protein?

Answer 12

The basal lamina and filtration slits

The fenestrae between the endothelial cells will let protein through

Question 13

How does the filtration barrier separate substances that are allowed to go into the Bowman’s capsule?

Answer 13

Size- small gets through

Electrical charge- (+) charges get through

Question 14

Are the filtration slits between podocytes just open hallways for shit to filter through?

Answer 14

No they are bridged by diaphragms

Question 15

How do you calculate GFR using the Starling Equation?

Answer 15

GFR= (Kf)(NFP)

NFP= [(Pgc-Pbc)-(ηgc-ηbc)]

Kf= filtration constant

Pgc and Pbc= hydrostatic pressure of glomerular capillary and Bowman’s capsule

ηgc and ηbc= osmotic pressure of glomerular capillary and Bowman’s capsule

(ηbc should be 0, since there should never be any protein getting through)

Question 16

How do you calculate the net filtration pressure (NFP) in the glomeruleus?

Answer 16

(Pgc-Pbc)-(ηgc-ηbc)

η= osmotic pressure of glomerular capillaryor Bowman’s capsule

P= hydrostatic pressure of capillary or Bowman’s cap

Question 17

what is Kf?

Answer 17

The filtration rate produced by each mmHg of net filtration pressure

Question 18

Which has a higher Kf:

Glomerular capillaries or regular capillaries

Answer 18

Glomerular capillaries have a Kf 50-100x greater

Question 19

Can Kf in the nephron be altered?

Answer 19

Yes, when the mesangial/M cells respond to angiotensin II, they will contract and reduce Kf.

(Therefore reducing GFR….but it will be balanced out by the kidney releasing prostaglandins)

Question 20

Which is the driving force for GFR:

Pgc

Pbc

ηgc

Answer 20

Pgc (the blood pressure in the glom capillary)

Question 21

What effect will increased Pbc (back pressure in Bowman’s capsule have on GFR?

Answer 21

Decrease GFR

Question 22

What effect will an increased ηgc have on GFR?

ηgc is the oncotic pressure of glomerular capillary blood

Answer 22

It will decrease GFR

Question 23

What happens to ηgc from the beginning of the capillary to the end?

Answer 23

It increases, as more water is drawn out of the blood and it is more concentrated

Question 24

Does Pgc change from the beginning of the capillary to the end?

Answer 24

No, it is constant.

The osmotic pressure of the capillary DOES change though (increases)

Question 25

What should ηbc always equal?

Answer 25

0

Should not be proteins in filtrate

Question 26

So as you move from the beginning of the capillary to the end, the pressure of the capilary stays the same, but the oncotic pressure of the blood increases. What does this do to NFP?

Answer 26

NFP will drop to zero by the end of the capillary

Question 27

Since the oncotic pressure of the capillary increases from beginning to end, does that mean that fluid is reabsorbed towards the end of the capillary?

Answer 27

No, it will never flow back into the capilary since the hydrostatic pressure of the blood remains so high

Question 28

When afferent and efferent arteriolar resistances increase, what happens to the hydrostatic pressure of the capillary blood?
What happens to RBF?

Answer 28

Pressure of the blood does not change

RBF decreases dramatically

(This is something that would happen if you were hemorrhaging blood)

Question 29

What effect will vasoconstriction at just the afferent arteriole have on Pgc and RBF?

Answer 29

Both will decrease

Question 30

What effect will vasoconstriction at just the efferent arteriole have on Pgc and RBF?

Answer 30

Pgc increases

RBF decreases

Question 31

What effect do NSAIDs have on prostaglandins?

Answer 31

Block their effects

Question 32

What do prostaglandins do for the kidney?

Answer 32

In response to SNS stimulation and subsequent vasoconstriction, as well as high levels of angiotensin II, they will vasodilate the afferent arterioles in order to maintain blood

Question 33

Where are the PGE2 and PGI2 prostaglandins made?

Answer 33

In the kidney

Question 34

How do NSAIDs affect RBF?

Answer 34

They prevent the synthesis of prostaglandins (COX inhibitors) and therefore interfere with the protective effects of prostaglandins on RBF.

Too many NSAIDs can starve the capillaries of blood flow